Neuroanatomy Cranial Nerves Continued In-Person Lecture Notes PDF

BMS Neuroanatomy Lecture 6 Cranial Nerves Continued (In-Person Class) Presented By: Dr. K. Lumsden; [email protected] (Toronto Campus) Dr. M. Doroudi; [email protected] Boucher Campus) CNs Overview Nerve Fiber Modalities for Cranial nerves: GSE: (General Somatic Efferent): motor fibers to skeletal m...

BMS Neuroanatomy Lecture 6 Cranial Nerves Continued (In-Person Class) Presented By: Dr. K. Lumsden; [email protected] (Toronto Campus) Dr. M. Doroudi; [email protected] Boucher Campus) CNs Overview Nerve Fiber Modalities for Cranial nerves: GSE: (General Somatic Efferent): motor fibers to skeletal musculature (VOLUNTARY) GSA: (General Somatic Afferent): fibers that carry general sensation (touch, pressure, pain, proprioception , temp, tickle and vibration) GVE: (General Visceral Efferent): motor fibers to smooth muscle, glands, and viscera (INVOLUNTARY) GVA: (General Visceral Afferent): fibers that carry visceralsensation BE/SVE: (Branchial Efferent/Special Visceral Efferent): motor fibers to skeletal, voluntary muscles that developed from branchial (pharyngeal) arches SVA: (Special Visceral Afferent): taste & smell SSA: (Special Somatic Afferent): vision, hearing & balance 3 Cranial nerve Rules: RULE #1 Parasympathetic GVE fibers reside ONLY in: CN III: Oculomotor CN VII: Facial CN IX: Glossopharyngeal CN X: Vagus These nerves have associated ganglion CN III = Ciliary Ganglion CN VII = Pterygopalatine & Submandibular Ganglion CN IX = Otic Ganglion CN X = Various ganglia near visceral organs 4 Parasympathetic Ganglia in Head & Neck Parasympathetic in Head & Neck Cranial nerve Rules: RULE #2 Branchial Motor (BE/SVE) fibers reside ONLY in nerves associated with pharyngeal (branchial) arches: 7 CN V - Trigeminal Nerve Major sensory nerve of the face Pathway: Begins at pons and travels superiorly/anteriorly towards face Splits into three terminal divisions at “trigeminal ganglion” in middle cranial fossa V1 = Ophthalmic V2 = Maxillary V3 = Mandibular Each terminal branch exits the skull via a different foramen and innervates a different region of the face 8 CN V; Trigeminal Ganglion CN V - Trigeminal Nerve V1 = Ophthalmic GSA Modality Upper face V2 = Maxillary V1 GSA Modality Mid face V3 = Mandibular GSA Modality Lower face BE/SVE Modality V2 V3 Arch 1 Muscles of mastication 10 1) Spinal nucleus of the trigeminal nerve: Pain the Tem & light touch. 2) Chief or principal nucleus or main sensory nucleus: discriminative sensation and light touch as well as conscious proprioception. 3) Mesencephalic nucleus: proprioception Trigeminal Sensory Nuclei CN V - Trigeminal Nerve V1 = Ophthalmic Pathway: Ophthalmic division passes through the cavernous sinus, exits via superior orbital fissure, & has many additional branches from there Foramina: Superior orbital fissure Function: GSA Modality General sensory to: forehead anterior scalp upper eyelid tip of the nose anterior nasal cavity frontal & ethmoidal sinuses dura mater of anterior cranial fossa V1 V1 Testing CN V1 = 1. Test sensation of forehead 2. CN V1 – corneal reflex 12 CN V - Trigeminal Nerve V2 = Maxillary Pathway: passes through the cavernous sinus, exits skull via foramen rotundum to innervate face Foramina: Rotundum Function: GSA Modality General sensory to: the sides of the nose lower eyelids upper lip posterior nasal cavity teeth of the upper jaw maxillary sinus nasopharynx palate dura of the middle cranial fossa V2 V2 Testing CN V2 = 1. Test sensation of lateral nose, cheek and upper jaw 13 CN V - Trigeminal Nerve V3 = Mandibular Pathway: not associated with cavernous sinus, exits skull via foramen ovale to innervate lower face Foramina: Ovale Function: GSA Modality General sensory to: lower lip chin lower face & cheek anterior external ear teeth of mandible mucous membranes of cheek anterior 2/3 of tongue dura in the middle cranial fossa V3 V2 V3 14 v The CN V extensively innervates the dura mater. v Headache due to referring pain from some pathological conditions in the head region! CN V - Trigeminal Nerve V3 = Mandibular Foramina: Ovale Function: BE/SVE Modality Arch 1 Voluntary motor control to muscles of mastication Temporalis Masseter Medial pterygoid Lateral pterygoid Collectively these muscles open/close the mandible for chewing action 16 CN V, SVE Component Ø The tensor tympani muscle, innervated by the mandibular branch of CN V, connects the auditory tube to the malleus handle. It increases the tension in the tympanic membrane, thus protecting it from excessive vibration in response to loud sounds. This muscle is contracted primarily to dampen the noise produced by chewing. Clinical Correlation: Trigeminal neuralgia Neuralgia: sensation of pain elicited without presence of noxious stimuli Often develops without any cause Intermittent attacks of severe, sharp, stabbing pain “electric shock” Most often affects CN V2 and V3 Affects GSA code only* No motor deficits Unilateral distribution Seen m/c in females (50+) Aggravated by: Exposure to cold Chewing Brushing teeth Talking Touching face Treatment usually involves medications which block incoming pain signals into CNS 19 Sensory Distribution of Trigeminal Nerve Trigeminal Nerve Pathways CN VII - Facial Nerve Foramina: Internal acoustic meatus AND Stylomastoid FIBER TYPES OF FACIAL NERVE: (BE/SVE, SVA, GVE, GSA) (1)BE/SVE axons to muscles of facial expression (arch II) (2) SVA axons (taste) from the anterior 2/3rds of the tongue (3) GVE axons to the submandibular, sublingual and lacrimal glands (4) GSA axons for the “patch” of skin behind the ear 25 CN VII - Facial Nerve Pathway: Facial nerve originates from the pons and first exits skull through the internal acoustic (auditory) meatus winding through the petrous portion of the temporal bone (facial canal) Infection in the middle/inner ear can impact CN VII Within temporal bone, nerve gives off several intracranial branches Remaining nerve will exit the cranial base via the stylomastoid foramen. FACIAL CANAL Foramina: Internal Acoustic Meatus AND Stylomastoid Foramen Once nerve exits skull – it gives rise to 6 extracranial branches 26 CN VII - Facial Nerve Intracranial branches: Chorda tympani carries GVE and SVA Branches off main nerve in the facial canal (inside skull) SVA = Special visceral afferent carrying taste perception from the anterior 2/3rds of the tongue GVE = General visceral efferent secretomotor of the submandibular and sublingual glands Via submandibular ganglion = Saliva production 27 CN VII - Facial Nerve Intracranial Branches: Greater petrosal nerve carries GVE Exits the petrous portion of the temporal bone where parasympathetic axons synapse in the pterygopalatine ganglion. GVE = General visceral efferent Secretomotor to lacrimal gland of eye (tear production) 28 CN VII, SVA Component 5- The primary gustatory region of the cortex is found in: the insula 1) 1st order Neuron 2) 2nd order Neuron 3) 3rd order Neuron CN VII, GVE Component CN VII - Facial Nerve Extracranial branches: BE/SVE Modality = Voluntary motor control to muscles of facial expression 5 branches: Temporal Zygomatic Buccal Mandibular Cervical “To Zanzibar By Motor Car” GSA Modality = GAS to skin behind the ear Posterior auricular branch 31 CN VII, SVE Component The Stapedius attaches to the stapes and helps to dampen sounds (i.e. protects from intense/loud sounds and dampens endogenous sounds such as chewing, talking, and swallowing). v Bell's Palsy results from trauma to the facial nerve, such as a viral meningitis infection. A wide variety of symptoms can manifest, including: Ø Weakness, twitching, or paralysis of facial muscles, including drooping of the eyelid and corner of the mouth. These symptoms would result from damage to the SVE portion of the facial nerve. Ø Dry eye or mouth. These symptoms would result from damage to the GVE component of the nerve. Ø Impairment of taste resulting from damage to the SVA component of the nerve. Corneal reflex: blinking an eye Reflexes of Cranial nerves Corneal Reflex = protects eyes from foreign bodies Sensory arc: CN V1 (touch to surface of cornea) Motor arc: CN VII (orbicularis oculi) Desired response = BILATERAL regardless of input side! TEST: Cotton gauze touched to cornea of R eye should result in blink/closure of BOTH eyes Clinical significance? Cotton gauze touched to L eye, only R eye blinks à means sensory signal worked, but L motor did not work Cotton gauze touched to L eye, and no eyes blink à means sensory input did not work What could dull this reflex, giving you a false positive? 35 CN VIII = Vestibulocochlear Nerve Two separate nerves that travel together Pathway: Begins at base of pons and exits cranium via internal acoustic meatus. Terminates as separate nerves in inner ear Foramina: Internal Acoustic Meatus Function: Special Somatic Afferent (SSA) for two senses: Hearing (Cochlear) Balance & equilibrium (Vestibular) 40 CN IX - Glossopharyngeal Nerve Pathway: Nerve emerges from the brainstem in the lateral medulla and exits the posterior cranial fossa through the jugular foramen. Majority of nerve remains extracranial to innervate structures of face and throat Foramina: Jugular foramen Function: Glossopharyngeal has five (5) modalities BE/SVE – voluntary motor SVA – special visceral afferent GVE – general visceral efferent GVA – general visceral afferent GSA – general somatic afferent 46 CN IX - Glossopharyngeal Nerve FIBER TYPES OF GLOSSOPHARYNGEAL NERVE: (1) BE/SVE axons innervate stylopharyngeus (swallowing muscle) (2) SVA axons carry taste perception from the posterior 1/3 of the tongue (3) GVE axons innervate the parotid gland via otic ganglion (secretomotor function) (4) GVA axons from the carotid body (visceral sensation from carotid body for chemoreception – maintaining BP) (5) GSA axons - sensory from skin posterior to the ear, posterior 1/3 of tongue, and the afferent part of the gag reflex 47 CN X - Vagus Nerve Pathway: Nerve emerges from the brainstem in the lateral medulla and exits the posterior cranial fossa through the jugular foramen. Foramina: Jugular foramen Function: Vagus nerve has five (5) modalities BE/SVE – voluntary motor SVA – special visceral afferent GVE – general visceral efferent GVA – general visceral afferent GSA – general somatic afferent 54 CN X - Vagus Nerve FIBER TYPES OF VAGUS NERVE: (1) BE/SVE axons innervate the majority of the muscles of the pharynx, larynx and soft palate (moving food towards esophagus during swallowing) (2) GSA axons from skin posterior to ear, dura in posterior cranial fossa, mucous membranes of pharynx & larynx (3) GVA axons from thoracic & abdominal viscera & aortic body Chemoreceptors – blood content Baroreceptors – blood pressure (4) SVA axons (taste) from the root of tongue and epiglottis region (5) GVE axons (parasympathetic) to thoracic and abdominal viscera up to left colic flexure. Synapse is in or around target organ. 55 CN X, Nuclei Clinical Correlation: Vagus Nerve injury Recurrent Laryngeal Nerve branch: BE/SVE– Branchial efferent / Special Visceral Efferent Nerve supplies muscles of the larynx/voice box Travels posterior to thyroid Common causes of injury: Tumor or after surgical intervention of the thyroid Bronchial carcinoma Aortic arch aneurysm Patient presentation includes: Hoarse voice Vocal changes (dysphonia) Difficulty producing speech On R side, loops around R subclavian a. On L side, loops around arch of aorta 58 CN X - Vagus Nerve GVE axons = Parasympathetic Outflow: TARGET RESPONSE HEART Decreased heart rate LUNGS Decreased respiratory rate DIGESTIVE SYSTEM (FOREGUT AND MIDGUT ORGANS): Esophagus, Stomach, Liver, Gall bladder, Spleen, Pancreas, Small intestine, Large intestine to proximal 2/3 transverse colon) Stimulate secretion of digestive enzymes from salivary glands, liver, pancreas, gallbladder, stomach Stimulate digestion and absorption of nutrients within alimentary canal up to the transverse colon Synapse in/around target organ Innervates smooth muscle and glands of the thoracic and abdominal viscera 59 CN X, GVE Component CN X, GVA Component q The gag reflex is initiated in response to stroking the back of the throat and is mediated by the vagus nerve Reflexes of Cranial nerves Gag Reflex = helps prevent choking Sensory arc: CN IX (touch to base of throat) Motor arc: CN X (motor response of pharynx) Desired response = BILATERAL regardless of input side! TEST: Touch one side of the oropharynx should result in contraction of soft palate muscles of BOTH sides (sometimes this can be elicited by just asking patient to say “ahhhh”) Clinical significance? CN X motor problem = uvula will deviate to the intact side (away from side of injury) CN IX sensory problem = NO RESPONSE (soft palate muscles do not contract at all) Protective response that prevents oral contents from entering the throat except as part of normal swallowing 63 CN XI = Spinal Accessory Nerve Pathway: Nerve begins at medulla and exits cranium via jugular foramen Foramina: Jugular foramen Function: voluntary motor to Sternocleidomastoid and Trapezius muscles SCM – contralateral rotation of head Traps – shoulder “raises” General Somatic Efferent (GSE) 68 CN XI, UMN Innervation of Trap & SCM CN XII = Hypoglossal Nerve Pathway: Nerve begins at medulla and exits cranium via hypoglossal canal Foramina: Hypoglossal canal Function: voluntary motor to muscles of the tongue General Somatic Efferent (GSE) 71 1 - Remember, the cortex normally send bilateral innervation to cranial nerve motor nuclei. The one exception is innervation of the genioglossus muscle, which is contralateral. CN XII = Hypoglossal Nerve Common causes of injury: Injuries are fairly rare Posterior neck dissection Fracture of atlanto-occipital joint Patient presentation includes: Tongue deviated to same side as injury due to atrophy of muscle muscles “lick your wounds” presentation Dysphagia (difficulty swallowing) Slurred speech Fasciculation on the tongue – “bag of worms” appearance Testing CN XII= “Stick out your tongue” 75